6. The Benefits of Lean Manufacturing: Single Piece Flow

“Lean manufacturing is a management philosophy that pursues the continuous elimination of waste in all business processes though kaizen, also known as small and incremental improvement.”

Many of us are familiar with this common definition of Lean. While it is certainly accurate, we often find that the specific benefits that Lean will have on individual processes and eventually entire companies are seldom discussed. While it makes sense that the elimination of waste will result in more efficient operations, in this article we explore what is achieved after much waste has been eliminated from a shop floor, notably single piece flow.

Single Piece Flow: Single piece flow can be described as an ideal state of efficient operations, where batch sizes and lot production are replaced by working on one product at a time. While not practical for operations which very low processing times and correspondingly high change-over times (both values defined by takt time), it is nevertheless a Lean Manufacturing goal to achieve single piece flow in every operation possible.

Achieving one-piece flow requires the elimination of waste. We remind the reader of the seven wastes:

Labor

Overproduction

Space

Defects

Unnecessary human motion

Inventory

Transportation

As a company reduces these wastes and strives for single piece flow, many other benefits will follow. Some of these benefits include (1) improved quality and fewer defects (2) reduced inventory (3) less space required to build product, (4) enhancement to overall manufacturing flexibility, (5) identification of future kaizen workshops, (6) ensures a safer work environment and (7) improves employee morale. We will review each of these benefits in more detail:

(1) Improved quality and fewer defects: When batching and lot production are eliminated, there is less opportunity to manufacture defects. Since the batch size will be just 1, there will not be mountains of inventory to count, move, store and pick.

Furthermore, single piece flow ensures that if there is a quality problem, we know that the defect has affected only that single part. We do not need to dedicate hours isolating and testing other material in the same production run to determine if it meets quality standards.

Of course, if a defect is caught in a single piece flow environment, this should not mean that we do not take the appropriate corrective actions to ensure that the problem will not reoccur. In this case, the manager or supervisor must determine if standard work was followed and if so, what changes need to be made to the standard in order to ensure that the problem will never resurface again. Kaizen!

(2) Reduced Inventory: Implementing single piece flow will require each operation to only produce what is needed by the next operation (in Lean jargon, we call this individual the surgeon). When followed properly, the process will eliminate any opportunity to build ahead. Consequently, inventories will not be allowed to build up.

(3) Requires less space: As inventory levels are reduced, less space and manpower will be required to manage (receive, count, stock, store, pick and deliver) it. In addition, single piece flow usually results in manufacturing cells which squeeze machines close together so that a single operator can oversee many pieces of equipment with the least amount of walking motion.

(4) Enhances overall manufacturing flexibility: We know from our value steam maps that the less inventory in a value steam, the shorter the lead-time will be from customer order to product delivery. In a single piece flow environment, since we operate with less inventory, lead-times will also drop, thereby giving us more time to react to customer orders (unless the strategic decision is made to pass off the lead-time gains to the customer in order to beat competitors!).

(5) Makes identifying future kaizens simpler: We have already discussed that in a single piece flow environment, defects and WIP inventories fall. As this happens, the shop floor will open up and it will become easier to see production problems. For example, if a particular process can not keep up with takt time and WIP is not allowed to be incurred, it will quickly become apparent to even the casual observer that something is wrong. In this case, it will be easy to decide where to focus the next improvement activity.

(6) Ensures a safer work environment: Less inventory means less clutter, more light in the darkest corners of the factory and the opportunity to better lay out equipment and tools. Also, since manufacturing cells are occupied by a set number of employees who each know their repeating tasks (as defined by standard work), there is less opportunity for unexpected movements, which increase the chances of accidents.

(7) Improves employee morale: Since single piece flow results in production problems being identified and (hopefully) solved right away, team members will receive immediate feedback on their work. This in turn will give everybody more ownership in their production area. Also, provided they lead problem solving efforts by focusing on processes and not individuals, more trust will be gained in managers.

These are just some of the benefits of single piece flow. Of course implementing such a production system is easy to write about or discuss in an academic context. Inside the plant, achieving single piece flow will require years of work. At a minimum, waste must be continually sought, standards (via 5S for example) must be implemented and maintained and a level loaded (haijunka) schedule must be developed. All this will require many hours of hard work and constantly challenging the current state.

Good luck! As always, do not hesitate to contact us if you have any questions or would like to provide feedback on this article.